Drainage and other trenches of various sizes and shapes are desirable for numerous applications. For example, manufacturing facilities typically require drainage systems which include trenches formed in the building floors to collect, remove and/or recycle excess water or other liquids. In addition, numerous outdoor industrial and commercial sites, such as parking lots, require drainage systems, including trenches, to collect and direct rainwater and other liquids to underground storm sewers to prevent flooding and to decrease runoff.
In the past, these trenches have generally been formed by first placing and securing a form of predetermined shape in a ditch which has previously been formed in the ground. A moldable trench forming composition, such as cement, concrete, or the like is then poured around the form and is allowed to set. Once the concrete has set, the form is removed from the resulting trench.
One common type of form assembly used to define a trench includes a wooden frame and strut structure. The wooden form includes a wooden frame which is covered with wooden sheets or planks to define a generally rectangular elongate trough. The wooden form is typically enclosed along its side and bottom faces, but may have an open top. Typically, a number of supporting wooden ribs are installed within the wooden form to increase the strength of the form so that it can withstand the relatively large pressures exerted by moldable trench forming compositions poured about it.
The wooden form is placed and secured within a preformed ditch. Concrete is typically poured up to the bottom face of the form and allowed to set. Then additional concrete is poured between the earthen walls of the ditch and the wooden sides of the form. Once all of the concrete has set, the wooden form is disassembled and removed from the trench.
Wooden forms are generally formed of lumber having a relatively rough exterior texture. Correspondingly, the inside surface of the trench formed by the wooden form is relatively uneven which reduces the efficiency of the flow of liquid through the trench. In addition, the assembly and disassembly of the wooden forms is both costly and labor intensive. The relatively large cost and labor required for assembly and disassembly of the wooden forms is increased in the formation of long trenches, and even further increased in the formation of trenches having a pitched or slanted bottom surface to facilitate drainage.
It is normally desirable to finish the trench with an elongate grate covering its open top in order to prevent people from unwittingly stepping in the open trench, to provide a smooth surface for vehicle travel, and/or to prevent relatively large objects from entering the trench and potentially blocking the flow of liquid therethrough. The grate is generally supported by a pair of spaced apart frame members which are set into and extend from the walls of the concrete trench. In order to stabilize the grate and to prevent the grate from rocking when weight, such as from a passing vehicle, is applied thereto, the frame members must be aligned in a common plane during the pouring and setting of the concrete about the form. If the grate is not properly aligned, the grate, the frame members and/or the concrete trench itself may be damaged by the resulting movement of the grate. If the grate rocks excessively, the grate may even be dislodged from the frame members thus leaving the trench exposed. Accordingly, the alignment of the frame members in the moldable trench forming composition is both important and laborious.
In an attempt to properly align the frame members without laborious manual alignment, precast trench assemblies have been developed. Precast trench assemblies generally include preformed metal and/or plastic assemblies designed to be placed in a preformed ditch. Moldable trench forming composition may thereafter be poured about the precast trench assembly. Once the trench forming composition has set, the precast trench assembly is securely bonded to the trench forming composition to stabilize and support the trench. Precast trench assemblies, however, are relatively expensive and may only be used once.
Commercially significant methods and apparatus for forming trenches, together with improved removable forms for forming trenches, are disclosed in U.S. patent application Ser. No. 07/768,610 to Stegall filed Sep. 26, 1991. In advantageous embodiments thereof inexpensive forms are employed to form trenches having properly aligned frame members. The trench forming assembly disclosed in U.S. patent application Ser. No. 07/768,610 preferably includes longitudinal frame members having a plurality of anchoring rods extending downwardly from the frame members. An elongate form body, preferably formed of relatively lightweight expanded polystyrene, preferably includes aligned longitudinal slots in the opposed side walls for receiving the frame members. Horizontal portions of the frame members are secured within the longitudinal slots in the sidewalls of the form body during formation of the trench so that the frame members are held in alignment during the trench forming operation. In typical practice, one or more wires are wrapped around the outside of the form body and frame members to hold the frame members in the slots of the form.
Preferably the assembled form and frame members are placed into a prepared ditch by suspending the assembly from its top. Concrete is first poured around the bottom of the anchoring legs attached to the frame members and allowed to set. Then concrete is poured around the form body and allowed to set. Finally the form body is removed to expose the resulting trench and the properly aligned frame members. The removal of the form is preferably facilitated by a pair of slots extending a relatively short distance into the form body from its bottom surface. Wires are provided in the slots and, once the trench forming composition has set, are pulled upwardly through the form. The form body is thereby cut into several pieces that can be more easily removed from the trench.
This system has greatly simplified the trench forming process and has achieved significant commercial success. In typical commercial practice, such form assemblies have been prepared on a custom basis by cutting one or more forms of desired shape and preparing frame members of desired length having anchoring legs welded thereto. These various parts have been assembled on-site using wires or other tying members to secure the frame members into the slots in the side surfaces of the form body. Due in part to the bulk and size of the frame member/welded anchoring leg portions of the assembly, shelf stocked inventories of the system have been limited.